1. Field of the Invention
The present invention relates to a thin type micro reforming apparatus used in a fuel cell, and more particularly, to an improved thin type micro reforming apparatus having a bubble remover in the evaporator to effectively remove bubbles formed during the vaporizing of liquid fuel, in order to prevent a pressure buildup within the evaporator and increase heat transfer efficiency. The improved thin type micro reforming apparatus also supplies liquid fuel in the form of droplets to be vaporized in the evaporator, thereby to prevent reverse flow caused by back pressure of the liquid fuel.
2. Description of the Related Art
A recent increase in the use of mobile phones, PDAs, digital cameras, laptop computers, and other small, portable electronic devices—and especially, the beginning of DMB broadcasting for mobile phones—has given rise to a need for more effective power supplies for portable, compact terminals. Lithium ion secondary cell batteries used widely today provide power for only 2 hours of DMB viewing. While efforts are underway to enhance their performance, the fuel cell is increasingly being viewed as a more viable solution to the above problem.
Such fuel cells include direct methanol type fuel cells that supply methanol directly to fuel electrodes, and reformed hydrogen fuel cells (RHFC) that extract hydrogen from methanol to supply to fuel electrodes. RHFC fuel cells use hydrogen as fuel, as in a polymer electrode membrane (PEM), and have the benefits of high output, power capacity available by volume unit, and no byproducts other than water. However, a reforming apparatus needs to be added to the system, making the device unsuitable for miniaturization.
To derive a high power output from such a fuel cell, a reforming apparatus must be used to convert liquid fuel to hydrogen gas fuel. This type of reforming apparatus includes an evaporator for converting liquid methanol to a gaseous form, a reformer that converts methanol fuel to hydrogen through catalytic conversion at a temperature between 250° C. and 290° C., and a CO remover (or a PROX) that removes the byproduct carbon monoxide. The reformer (that reacts to absorb heat) should be maintained at a temperature between 250° C. and 290° C., the CO remover should be maintained at a constant temperature between 170° C. and 200° C., in order to produce optimum reaction efficiency.
As shown in FIG. 1, a conventional reforming apparatus 250 is disclosed in Japanese Patent No. 2003-048701, which is hereby incorporated by reference. This conventional compact reforming apparatus 250 has an evaporating chamber 252 within which a cavity 254 is disposed, and an evaporating heater 256 provided on the cavity 254. Also, a fuel injector 258 is provided in the cavity 254. The fuel injector 258 injects a mixture of methyl alcohol fuel and water into the cavity 254. This injected liquid fuel mixture 260 is heated and vaporized by the evaporating heater 256. The gas formed by the vaporized liquid fuel mixture 260 flows into micro passages 262, and is reformed into hydrogen and carbon dioxide by means of reformer catalytic converters 264 installed in the micro passages 262.
This conventional reforming apparatus provides the fuel injector 258 at the fuel supply conduit to increase the efficiency of the evaporator by widening the surface area of the fuel to increase vaporizing speed. Also, by using the fuel injector 258 to inject fuel, the liquid fuel mixture 260 is separated into droplets, increasing the surface area of the volume of fuel for the reforming apparatus, so that the reforming efficiency of increases for the same quantity of fuel.
However, this conventional reforming apparatus must be installed around the fuel injector 258, and the quantity of fuel injected through the fuel injector 258 must be controlled by a separately installed controller. Accordingly, not only is this conventional configuration of a reforming apparatus 250 complex, it is also difficult to miniaturize.
As shown in FIG. 2, another conventional reforming apparatus 300 is disclosed in Japanese Patent No. 2004-275807, which is hereby incorporated by reference. This type of reforming apparatus 300 has a plurality of heated medium passages 305 installed therein (through which a heated medium such as gas passes), and a first heating plate 312 and an adjacent second heating plate 313 that are heated by the heated medium passing through the heated medium passages 305. The second heating plate 313 has an evaporated liquid passage 316 with a passage width d2, and the evaporated liquid passage 316 has a plurality of protruding fins 317 formed with a height d1 on the side thereof. Because the height d1 of the fins 317 is less than the width d2 of the passage, the bubbles created by the evaporating liquid can easily expand past the fins 317 and increase heat transfer efficiency by forming a thin layer of the evaporated liquid.
That is, this conventional method installs the fins 317 having a height of approx. 30% or less of the width of the channel, so that when evaporation occurs, the bubbles created can expand along the fins 317 to form a thin layer on the insulating surface to efficiently transfer heat. However, because the height of the fins 317 and the width of the passage must be formed in different dimensions, either dry etching must be performed twice or the manufacturing process becomes difficult.
As shown in FIG. 3, another conventional reforming apparatus 400 is disclosed in Japanese Patent No. 2004-89748, which is hereby incorporated by reference. This conventional structure, an evaporator 403 is disposed on one side of a substrate 401 on which a passage extends, a reforming portion 404 and a CO removing portion 405 are successively disposed downstream along the passage, and a hydrogen discharge port 410 is disposed further downstream. However, in this conventional structure, although a passage extends from the evaporator 403, gas formation that occurs when liquid fuel is vaporized cannot be prevented.
Thus, in conventional reforming apparatuses, as fuel is vaporized in the evaporators, a sudden expansion occurs where bubbles are formed within the evaporator to increase pressure. The increase in pressure causes back pressure towards the fuel input portion to prevent further supply of fuel. Therefore, an improved structure for an evaporator is needed.